Year ago I could easily hit 60-70+ FPS and even 100 FPS at medium-crowded places.
Today I can't even hit 50 FPS with a bit of environment around me.
And not even 100 FPS when there's almost literally nothing around me.

I even use 640x480 to reduce lag, but it's as the same as the normal resolution I use 1280x800.

Already tried everything, I don't want download links to modifications which make you lag less.
Already tried that NVIDIA visualizer and disabled that E-stuff.

It's impossible for you to have only one GPU. You talked about having a Nvidia one so that's one and your CPU also has integrated graphics. That's probably your problem. If you're playing while not plugged in to the wall, try it while your laptop is connected to electricity and not running on battery. Also check what's your battery mode on, if it's on power saving or balanced, set it to performance.